Stonefly Nemoura cinerea. Left: adult Right: nymph showing the long posterior cerci, and the externally developing wings.
Although most adult stoneflies have wings, they are weak fliers and they usually crawl, rather than fly. Stonefly adults and nymphs are more active at night but they can be found during the day resting on waterside vegetation or sitting on rocks in or near water. The nymphs live in streams, rivers and lake margins, where they feed on algae, diatoms and decaying vegetation. In some species the older nymphs become predators of other small aquatic animals. Fly-fishers tie imitation stonefly nymphs to hook trout when the nymphs are active.
Female stoneflies gather their eggs into a ball and hold them on the underside of their abdomens until they are ready to release the eggs into the water. The life cycle is usually completed in one year but some species developing in cold upland streams may take two or more years to complete the nymphal stages. When the nymphs have completed their development, they crawl out of the water. The adult stonefly emerges from the final nymphal instar and is able to expand its wings.
Role of stoneflies in gardens
A typical garden pond is an unsuitable habitat for most stonefly species, so this type of insect is not often seen in gardens. If you do encounter one in your garden, please let us know.
Other sources of information
David Pryce (2005) Stoneflies Salmo trutta 8: 41- 44 Available here
Dobson,M. Pawley,S. Fletcher,M. & Powell, A. (2012) Guide to Freshwater Invertebrates Published by Freshwater Biological Association
Hynes, H. B. N. (1977) Adults and nymphs of British stoneflies (Plecoptera). Freshwater Biological Association
Pryce, D., Macadam, C. & Brooks (2007) Guide to British stonefly (Plecoptera) families: Adults and larvae. Field Studies Council
Page text drafted by Andrew Halstead, reviewed by Andrew Salisbury, compiled by Steve Head